Mount additional volumes to 'postgres' container when 'targetContains` is an empty list (#1475)

* Mount additional volumes to 'postgres' container when 'targetContainers' is an empty list

Co-authored-by: Felix Kunde <felix-kunde@gmx.de>

Co-authored-by: Felix Kunde <felix-kunde@gmx.de>

pkg/cluster/k8sres.go

@@ -1452,7 +1452,7 @@ func (c *Cluster) addAdditionalVolumes(podSpec *v1.PodSpec,
 			continue
 		}
 
-		if v.TargetContainers == nil {
+		if len(v.TargetContainers) == 0 {
 			spiloContainer := podSpec.Containers[0]
 			additionalVolumes[i].TargetContainers = []string{spiloContainer.Name}
 		}